The wide scale deployment of insecticide-based interventions against adult mosquito vectors has contributed to significant declines in the global malaria burden in recent years. However, many malaria-affected countries are now reporting the emergence of insecticide resistance. If left unchecked, the spread of resistant mosquitoes could derail contemporary malaria control. Yet surprisingly, the epidemiological significance of insecticide resistance remains very poorly defined and examples demonstrating a causal link between resistance and malaria resurgence are few. Our overall objective in the current proposal is to determine whether and how insecticide resistance ultimately affects malaria transmission. Specifically we aim to determine the extent to which mosquitoes nominally defined as resistant using the `industry standard' WHO assays, remain functionally resistant when the influence of a suite of ecological factors such as insect age, infection status, environmental conditions, realistic exposure patterns and insect behavior are taken into account. To complement these transmission-related measures, we will quantify any fitness related costs associated with insecticide resistance, again capturing the effects of realistic environmental stressors. Finally, we will use a suite of modeling approaches parameterized from the novel empirical data to explore the implications of resistance for malaria transmission and to evaluate how resistance might spread under different environmental conditions and possible management prescriptions. Combined, the research will advance fundamental understanding of the epidemiological significance of insecticide resistance and provide an evidence base for appropriate development of insecticide resistance management strategies.